1. Field of the Invention
The present invention relates to an exposure method and apparatus, and device manufacturing method. More particularly, the present invention relates to an exposure method used when a semiconductor device, liquid crystal display device, or the like is manufactured in a lithographic process, an exposure apparatus to which the exposure method is applied, and a method of manufacturing devices such as semiconductor devices and liquid crystal display devices by using the exposure method or apparatus.
2. Description of the Related Art
Conventionally, in a lithographic process for manufacturing a semiconductor device, a liquid crystal display device, or the like, an exposure apparatus has been used. In such an exposure apparatus, patterns formed on a mask or reticle (to be generically referred to as a xe2x80x9creticlexe2x80x9d hereinafter) are transferred through a projection optical system onto a substrate such as a wafer or glass plate (to be referred to as a xe2x80x9csubstrate or waferxe2x80x9d hereinafter, as needed) coated with a resist or the like.
As apparatus of this type, a static exposure type (also called a step-and-repeat method) reduction projection exposure apparatus (a so-called stepper) and a scanning exposure apparatus based on a step-and-scan method have been put into practice. The stepper is designed to repeat stepping operations which positions a wafer stage on which a wafer as a substrate is mounted to a predetermined exposure position by moving the stage two-dimensionally by a predetermined amount. And while the wafer stage is positioned, exposing operations of transferring a reticle pattern onto a shot area on the substrate through a projection optical system is repeated. The scanning exposure apparatus is an improvement of the stepper. This apparatus is designed to synchronously move a reticle stage holding a reticle and the wafer stage in a predetermined scanning direction with respect to the projection optical system while illuminating a predetermined slit-shaped area on the reticle with an illumination light. The overall reticle pattern is transferred onto the respective shot areas on the wafer by sequentially transferring the pattern formed on the reticle in the slit-shaped area, onto the wafer through the projection optical system.
In these exposure apparatus, shot areas are arranged on a wafer at predetermined intervals in rows and columns, in a shape of a matrix (no shot areas are actually formed on the first layer, but in this case virtual shot areas are included) are exposed in a predetermined sequence. As the predetermined sequence, from the view of the moving efficiency of the wafer stage in exposure, which leads to an improvement in the throughput of the apparatus, a so-called row zigzag method or column zigzag method is generally used. In this case, the row zigzag method is a method of the exposure apparatus exposing respective shot areas arranged on the wafer in the shape of a matrix by sequentially stepping in the X direction (or in the Y direction) by a predetermined amount along a row. And on exposing the next row, the apparatus sequentially performs stepping operation in a reverse direction (parallel and reverse direction to that on the preceding row). In the column zigzag method, the xe2x80x9crowsxe2x80x9d in the row zigzag method are respectively replaced with xe2x80x9ccolumnsxe2x80x9d, and xe2x80x9ccolumnsxe2x80x9d with xe2x80x9crowsxe2x80x9d. Accordingly, in this specification, the terms xe2x80x9crow zigzag methodxe2x80x9d and xe2x80x9ccolumn zigzag methodxe2x80x9d are hereinafter used as in the meanings described above.
On exposing the second or subsequent layers, positioning (hereinafter to be referred to as alignment) of the circuit patterns on the shot areas formed on the wafer by exposure of the preceding layer and the reticle pattern is performed. Alignment methods include the die-by-die method and the enhanced global alignment (to be referred to as xe2x80x9cEGAxe2x80x9d hereinafter) method which details are disclosed in U.S. Pat. No. 4,780,617. In the die-by-die method alignment is performed shot by shot. Whereas, in the EGA method the alignment marks (positioning marks transferred together with circuit patterns) are measured at a plurality of positions within the wafer. The array coordinates are then obtained of the respective shot areas by the least-squares approximation or the like, and stepping is performed by using the calculated result in accordance with the precision of the wafer stage on exposure. Of these methods, the EGA method is widely used from the aspect of throughput of the apparatus.
With the conventional exposure apparatus, on changing a shot area subject to exposure, when the first layer is exposed, the stepping amount in the row direction is determined as an integer multiple of a predetermined row interval. And the stepping amount in the column direction is set to an integer multiple of a predetermined column interval. On exposure of the second or subsequent layer that uses the EGA scheme, the stepping amount is obtained from the calculation result of the EGA.
However, determining the stepping amount conventionally by using the EGA method limited the overlay accuracy between layers. This was because the wafer gradually expanded due to irradiation thermal energy on exposure.
That is, on exposing a shot area on a layer, thermal energy is generated by the reaction of the resist coated on the wafer or by the so-called excessive optical energy which did not serve as the energy for the reaction of the resist. As a result, the wafer temperature rises. Although some of the thermal energy generated dissipates from the wafer surface into the atmosphere, most of the thermal energy stays in the wafer. The remaining thermal energy conducts through the wafer, and to the wafer holder from the rear surface of the wafer. The thermal energy is gradually conducted through the wafer reaching the holder through the lower surface of the wafer. And, the thermal energy conducted to the wafer holder circulates within the wafer holder. That is, the wafer and the wafer holder are heated together. Furthermore, since the rear surface of the holder, i.e., the opposite surface side of the surface in contact with the wafer is in contact with the wafer stage, therefore, the thermal energy is also gradually transmitted to the wafer stage.
In this process, the balance of the energy gradually moves toward the tendency in which the thermal energy is stored in the wafer and wafer holder. More specifically, the wafer and the wafer holder gradually store the thermal energy, from the beginning of exposure on the first shot area (the first shot area) on a layer until exposure of the last shot area is completed. That is, the temperature of the wafer and wafer holder gradually rise, therefore, the wafer and wafer holder gradually expand. Since the linear expansion coefficient of a Si wafer is 2.4 ppm/k, a wafer having a diameter of 20 mm expands as large as 48 nm while the temperature rises 0.1xc2x0 C.
Consequently, on exposure with a conventional exposure apparatus, in general, the intervals between adjacent shot areas in a cooled state after exposure become smaller than of the designed interval as the exposure sequence proceeds. As a result, the difference between the shot area intervals in a cooled state after exposure and the designed interval lose its uniformity on the substrate. In addition, depending on the exposure sequence such as the row zigzag method or column zigzag method, the state losing its uniformity varies.
In general, on forming a semiconductor circuit, a lithographic process of 20 or more layers is required, and in each processing the overlay accuracy with its preceding layer is significant. The alignment error described above, is, naturally, a factor of this overlay error. However, even if the alignment is successfully performed, there is no guarantee that overlay between layers will be successful. This is because the reticle on which the circuit pattern is drawn and which is used to form each layer differs in transmittance and reflectance depending on the shape of the pattern drawn, and hence the energy that reaches the wafer vary in level. In addition, the reflectance of the wafer surface may differ depending on the layers, as well as the resist coated on the wafer surface may differ in type, thickness, and the like. Accordingly, since the expansion amount of the wafer may differ depending on the layers, even if the exposure shot sequence is the same as that of the preceding layer, an offset may be caused between layers.
Furthermore, if the exposure sequences is different between layers, e.g., a sequence based on the row zigzag method is used for exposing the preceding layer and a sequence based on the column zigzag method is used for exposing the next layer, the overlay error of a pattern between layers increases.
The present invention has been made in consideration of the above situation, and has as its first object to provide an exposure method, which can improve overlay accuracy.
It is the second object of the present invention to provide an exposure apparatus, which can improve overlay accuracy.
It is the third object of the present invention to provide a method of manufacturing high-integrated devices with increased productivity.
According to the discoveries made by the present inventor on many years of research, when a plurality of divided areas on a substrate such as a wafer are exposed without any consideration of thermal expansion of the substrate which changes due to the conductance of thermal energy within the substrate or from substrate to holder or within the substrate holder, the position of the divided areas deviate from the designed values when it resumes the cooled state after exposure. The distribution of such deviations on the wafer depends on the exposure sequence or the speed of exposure sequence in the divided areas. In this specification, the thermal expansion of the substrate also includes a state where there is a substrate holding member or the like which measures the thermal expansion of the substrate as a single unit. In such a case, the thermal expansion refers to the general thermal expansion of both the holding member and the substrate.
Therefore, in order to reduce the deviation between the position of the divided areas on the substrate and the designed position of the divided areas in a cooled state after exposure, a correction must be made in the movement amount when the substrate has completed an exposure of a divided area, and moves to expose the next divided area. This correction is made in consideration of the exposure sequence and its proceeding speed in the divided areas. Such corrections are to be made with respect to the deviation distribution on the substrate from the designed position of the divided areas in a cooled state after exposure. The present invention has been made with focus on this point.
According to the first aspect of the present invention, there is provided a first exposure method which sequentially transfers a pattern formed on a mask onto a plurality of divided areas arranged on a substrate along a predetermined direction, in an exposure sequence that proceeds to an adjacent divided area in the predetermined direction, and the exposure method comprises: correcting a movement information so as to make a correction amount of a movement amount of the substrate smaller than a correction amount of a movement amount of the substrate on preceding exposure, and adjusting a positional relationship between the mask and the substrate for exposure of a next divided area; and exposing the next divided area.
In this case, other than correcting the movement amount of the substrate, xe2x80x9ccorrecting a movement informationxe2x80x9d includes a correction which result is equivalent to correcting the movement amount of the substrate by adjusting the positional relationship between the substrate and the mask. For example, xe2x80x9ccorrecting a movement informationxe2x80x9d includes correcting a target position when the substrate shifts between divided areas and correcting the movement amount or the movement target position of the mask. In addition, the correction includes correcting of the rotational angle of the mask around a normal to the surface on which the mask pattern is formed, and the correction of the substrate movement can be combined with the correction of the mask movement. Furthermore, xe2x80x9ccorrecting a movement informationxe2x80x9d includes optically shifting an image of a pattern formed on the mask and electron-optically shifting the image by, for example, adjusting the deflection amount of an electron beam. The correction of an image pattern shift and the correction of the mask or substrate movement can also be combined.
For example, when the exposure sequence is based on the row zigzag method which is a type of exposure sequence used in the first exposure method according to the present invention, thermal energy generated by exposure on each preceding row spreads in the overall substrate as the exposure sequence proceeds from the first, second, third and subsequent rows. Accordingly, the thermal expansion of the substrate gradually increases. However, on considering exposure on a divided area immediately after moving to a new row, the divided area in the new row is temporally close to the divided area that has completed exposure in the preceding row and is thus spatially close. The tendency, in which the divided area that has become subject to exposure on the preceding row temporally close is spatially close to a divided area to be exposed decreases as the exposure in the new row proceeds.
As the exposure sequence in the predetermined direction proceeds, when the movement velocity of an exposure position in the predetermined direction (row direction) is not sufficiently slower than the conductance of thermal energy in the wafer, thermal expansion due to the energy generated by exposure on a divided area is supposed to occur first close to the divided area. Then, the overall substrate is likely to gradually expand due to the generated thermal energy. For this reason, on exposing one row, thermal expansion may gradually decrease as a new divided area becomes subject to exposure along the row direction.
In the first exposure method of the present invention, considering the situation, the movement information is corrected so as to make the correction amount of the movement amount of the substrate in the predetermined direction as the exposure proceeds, smaller than the correction amount of the movement amount of the substrate on preceding exposure thereby adjusting a positional relationship between the mask and the substrate for exposure of a next divided area. This makes it possible to ensure high overlay accuracy.
In the first exposure method according to the present invention, in the case the divided areas are arranged on the substrate in a shape of a matrix, the exposure sequence proceeds to the adjacent divided area in a first row direction of the matrix, and when there is no adjacent divided area in the first row direction then goes on to an adjacent row in a column direction of the matrix, and continues in a second row direction which is opposite to the first row direction, and the correction amount of the movement amount of the substrate can be increased as exposure sequence proceeds to the adjacent row in the column direction. In this case, the first and second row directions are parallel to each other, and opposite in direction.
When exposure is performed in this sequence, many divided areas are exposed after moving in the column direction to change to the current row, and then the sequence proceeds to a new row in the column direction. In this case, the time interval is large between the former and the latter movement of changing rows. Therefore, the influence caused by local thermal expansion in the former movement is similar to the influence caused in the latter movement, however, the overall thermal expansion of the substrate is larger than when the former movement was performed. As the exposure sequence proceeds, therefore, high overlay accuracy can be maintained by increasing the correction amount of the movement of the substrate when a new row of the matrix is subject to exposure.
In the first exposure method according to the present invention, the movement information can be obtained prior exposure on the substrate.
On performing exposure of a multilayer, prior to actually exposing the second or subsequent layer, the movement information can be obtained by detecting positional information of a plurality of predetermined alignment marks which are among a plurality of alignment marks formed on the substrate with the plurality of divided areas; and obtaining positional information of the plurality of divided areas formed on the substrate by statistical calculation based on a result of the detecting. That is, the movement information can be obtained which is corrected based on the alignment measurement results by EGA as described above.
Based on the positional information of a plurality of divided areas, if, for example, a divided area interval is to be obtained as a movement information, the substrate is moved so that the obtained divided area interval is corrected to a new movement amount as a target movement amount in a predetermined direction. When, for example, the coordinate position of each divided area is to be obtained as a movement information, each coordinate position is corrected to a new coordinate position (e.g., a scanning start position in scanning exposure) as a target position, and the substrate is moved.
In addition, the substrate may be moved in accordance with the position information (coordinate position, divided area interval, or the like) of each divided area obtained by the EGA method, and the position of the mask may be corrected by an amount corresponding to a correction amount for the position of each divided area which is obtained as the movement information.
In the alignment method using statistical calculation, including the EGA method, designed positional information (coordinate position, divided area interval, or the like) may be corrected, as well as the calculation result, in consideration of the thermal expansion, and statistical calculation may be performed by using the corrected designed positional information.
In the first exposure method according to the present invention, the correction amount of the movement information can be determined in consideration of thermal expansion of the substrate when the substrate is moving.
In this case, since the temperature of the substrate changes each time the divided area is exposed, and the substrate expands differently, the correction amount of the movement information is determined based on the state of thermal expansion of the substrate when a new divided area is actually subject to exposure. The positional relationship between the substrate and the mask is then adjusted for exposing the next divided area by using the new movement information obtained by correcting the former movement information. This makes it possible to perform exposure so that the divided areas are arranged on the substrate at desired intervals, in a cooled state after the exposure. As a consequence, the overlay accuracy with respect to the next layer can be improved, while performing exposure with high overlay accuracy with respect to the preceding layer.
With a substrate, in practice, the diffusion speed of thermal energy generated by exposure is not very high, and thermal expansion due to thermal energy generated by exposure on a divided area locally occurs near the divided area first. The overall substrate then gradually is affected by thermal expansion. That is, it takes a long time to diffuse heat in the substrate.
Therefore, the correction amount of the movement information can be determined on an assumption that of an exposure already performed on a predetermined layer, a thermal energy generated on an exposure which is performed spatially and temporally close to an exposure to be performed on the divided area causes a local thermal expansion of the substrate, and a thermal energy generated on an exposure which is performed spatially and temporally far away from the exposure to be performed causes thermal expansion of the substrate in general. In such a case, since exposure is performed with careful consideration to the actual thermal expansion of the substrate, the overlay accuracy can be further improved.
In the first exposure method according to the present invention, prior to exposure on the substrate measurement patterns can be sequentially transferred on a plurality of measurement divided areas on a measurement substrate in accordance only with designed intervals between the measurement divided areas before transferring of the measurement substrate; and measurement substrate on which the measurement patterns are transferred can be cooled to a temperature prior to the transfer, and distances can be measured in between the measurement divided areas; and the correction amount of the movement information can be determined based on a result of the measurement.
In this case, prior to exposure for manufacturing devices, the state of thermal expansion of the substrate is measured by test exposure. This test exposure is performed by transferring measurement patterns formed on a measurement mask onto a plurality of measurement divided areas on the measurement substrate on based on only the design measurement divided area interval before the pattern is transferred onto the measurement substrate. In this case, it is preferable that the measurement mask, the measurement pattern, the measurement substrate, the measurement divided areas, the exposure sequence, and the like in test exposure are identical to those in the actual device manufacturing process.
The temperature before transfer may be set to a temperature when the substrate is loaded on the substrate stage on exposure. The measurement substrate may or may not be cooled by using a cooling unit. Alternatively, the measurement substrate may be cooled to the temperature before transfer through a process (PEB, cooling, and the like) identical to that in actual exposure. With the latter case in particular, since the measurement substrate receives the same thermal influence as in actual exposure, thermal expansion of the substrate can be accurately obtained. This makes it possible to ensure high overlay accuracy.
After the measurement substrate having completed test exposure is cooled, the patterns transferred on the measurement substrate are observed, thereby measuring the distances between the measurement divided areas. The measurement result reflects the thermal expansion of the substrate during exposure. The thermal expansion of the substrate due to exposure is then obtained based on the distance measurement result. As a consequence, extremely high overlay accuracy can be ensured. The patterns transferred on the measurement substrate may be latent images, resist patterns, or patterns after etching.
As the divided areas on the substrate are sequentially exposed, thermal expansion of the substrate progresses, as described above. In addition, distortion occurs on the substrate, as well as thermal expansion. Therefore, if a pattern formed on a mask is transferred onto a substrate through the projection optical system without changing the image magnification, the pattern transferred on the respective divided areas on the substrate which is cooled after exposure, may vary in size (e.g., the line width or the like of circuit patterns). In addition, the transferred pattern may be distorted on the substrate that is cooled after the exposure.
Accordingly, in the first exposure method according to the present invention, the image characteristic of a transferred image of the pattern onto the substrate is controlled based on the correction amount of the movement information. In this case, the size of the pattern transferred on the respective divided areas on the substrate that is cooled after the exposure can become identical, and distortion of the transferred patterns can be suppressed. This makes it possible to ensure high overlay accuracy throughout the surface of the divided areas. When a pattern on a mask is transferred onto a substrate through the projection optical system, by controlling the imaging characteristics of the projection optical system the image characteristics of the pattern image transferred onto the substrate can be controlled. The image characteristics of the transferred image of the pattern may be also be controlled by adjusting the positional relationship between the mask and the projection optical system.
In a scanning exposure in which a pattern formed on a mask is transferred onto a substrate while the mask and substrate are synchronously moved, the image magnification in the scanning direction is determined by the moving velocity ratio of the mask and the substrate. If, therefore, a pattern formed on a mask is transferred onto a substrate without changing the moving velocity ratio of the substrate and the mask, the pattern transferred onto the respective divided areas on the substrate that is cooled after the exposure, vary in size.
In addition, as described above, when the proceeding speed of an exposure sequence for divided areas is high, thermal expansion does not uniformly occur in the substrate, and does not occur in the same manner in exposure of respective layers.
Based on this situation, in the first exposure method according to the present invention., in the case the pattern formed on the mask is transferred onto the substrate while synchronously moving the mask and the substrate, at least one of a starting position of the mask which moves synchronously on exposure of the divided area, a starting position of the substrate which moves synchronously, a synchronous velocity ratio between the mask and the substrate, a direction of the mask moving synchronously, a direction of the substrate moving synchronously, and a rotational angle of the mask around a normal to a surface which the patterns are formed, can be corrected with respect to the correction amount of the movement information. With this method, the size of the pattern transferred onto the respective divided areas on the substrate that is cooled after the exposure can be identical in the scanning direction, and distortion of the pattern image transferred onto the substrate can be suppressed. This makes it possible to ensure high overlay accuracy.
In the case of using a projection optical system on scanning exposure, the image magnification of the pattern in the non-scanning direction (i.e., a direction perpendicular to the scanning direction) is corrected by changing imaging characteristics such as the projection magnification of the projection optical system, the distance between the mask and the projection optical system. This makes it possible to make the size of the pattern transferred onto the respective divided areas on the substrate that is cooled after the exposure identical, and suppress the occurrence of distortion of pattern images transferred on the substrate.
According to the second aspect of the present invention, there is provided an exposure method which sequentially transfers a predetermined pattern on a plurality of divided areas arranged on a substrate in a shape of a matrix in a sequence that proceeds to an adjacent divided area in a first row direction of the matrix, and when there is no adjacent divided area in the first row direction then goes on to an adjacent row in a column direction of the matrix, and continues in a second row direction which is opposite to the first row direction, the exposure method which comprises: correcting a movement information so as to make a correction amount of a movement amount of the substrate larger than a correction amount of a movement amount of the substrate on a preceding movement between rows, and adjusting a positional relationship between the mask and the substrate for exposure of a first divided area on a new row; and transferring a pattern onto the first divided area on the new row.
On performing exposure based on the second exposure method according to the present invention, after changing rows by moving in the column direction and exposing many divided areas, it then moves in the column direction to proceeds to a new row subject to exposure. Most of the thermal energy generated by exposure performed between the preceding row changing movement and the new row changing movement, therefore, is sufficiently diffused. As a result, the overall thermal expansion of the substrate in the new row changing movement is larger than that of the substrate in the preceding row changing movement. Accordingly, in the second exposure method according to the present invention, as the exposure sequence proceeds, correction of the latter movement of the substrate proceeding to new rows is made larger than the correction amount of the preceding movement. This makes it possible to maintain high overlay accuracy.
As in the first exposure method according to the present invention, in the second exposure method according to the present invention, the movement information can be obtained prior to exposure on the substrate.
Also, as in the first exposure method according to the present invention, in the second exposure method according to the present invention, the correction amount of the movement information can be determined in consideration of the thermal expansion of the substrate when the substrate is moving.
With this exposure method, the correction amount of the movement information can also be determined based on thermal energy generated by an exposure already performed on a predetermined layer on the substrate. In this case, the correction amount of the movement information can be determined by a function using a number of divided areas in which exposure is already performed on the predetermined layer as a variable. In addition, similar to the first exposure method according to the present invention, the correction amount of the movement information can also be determined on an assumption that of an exposure already performed on the predetermined layer, a thermal energy generated on an exposure which is performed spatially and temporally close to an exposure to be performed on the divided area causes a local thermal expansion of the substrate, and a thermal energy generated on an exposure which is performed spatially and temporally far away from the exposure to be performed causes thermal expansion of the substrate in general.
As in the first exposure method according to the present invention, in the second exposure method according to the present invention, prior to exposure on the substrate, the method can further comprise: transferring sequentially measurement patterns on a plurality of measurement divided areas on a measurement substrate in accordance only with designed intervals between the measurement divided areas before transferring of the measurement substrate; cooling the measurement substrate on which the measurement patterns are transferred to a temperature prior to the transfer, and measuring distances in between the measurement divided areas; and determining the correction amount of the movement information based on a result of the measurement.
Like the first exposure method according to the present invention, in the second exposure method according to the present invention, in order to reduce the difference between the size of pattern transferred onto the respective divided areas or suppress distortion of the transferred patterns on the substrate that is cooled after exposure, an image characteristic of a transferred image of the pattern onto the substrate can be controlled based on the correction amount of the movement information.
According to the third aspect of the present invention, there is provided a third scanning exposure method which sequentially transfers a pattern formed on a mask onto a plurality of divided areas arranged on a substrate while synchronously moving the mask and the substrate, the exposure method comprising: controlling a condition for scanning exposure on a predetermined layer in accordance with thermal energy generated by an exposure already performed on the predetermined layer on the substrate.
In a scanning exposure method like the third exposure method according to the present invention, an image magnification in the scanning direction is determined by the moving velocity ratio of a substrate and a mask. Therefore, when a pattern formed on a mask is transferred onto a substrate without changing the moving velocity ratio of the substrate and the mask, the pattern transferred onto the respective divided areas on the substrate that is cooled after the exposure, vary in size.
Also, distortion due to thermal expansion does not uniformly occur in a substrate, and does not occur identically in the respective layers.
Furthermore, the arrangement of the divided areas on the substrate that is cooled after the exposure deviates from a desired layout due to the thermal expansion of the substrate during the exposure.
In the exposure method according to the present invention, therefore, a condition for scanning exposure is controlled in accordance with the thermal energy generated by exposure that has already been performed on a predetermined layer on a substrate. The condition for scanning exposure, is at least one of a starting position of the mask which moves synchronously on exposure of the divided area, a starting position the substrate which moves synchronously, a synchronous velocity ratio between the mask and the substrate, a direction of the mask moving synchronously, a direction of the substrate moving synchronously, and a rotational angle of the mask around a normal to a surface which the patterns are formed, is corrected with respect to the correction amount of the movement information.
According to this method, the size of the pattern transferred onto the respective divided areas on the substrate that is cooled after the exposure can be identical in the scanning direction. In addition, distortion of pattern images transferred on the substrate can be suppressed. Furthermore, the deviation of the divided area arrangement on the substrate that is cooled after the exposure from the desired layout can be suppressed. Therefore, high overlay accuracy can be ensured.
According to the fourth aspect of the present invention there is provided a fourth exposure method which sequentially transfers a pattern formed on a mask onto a plurality of divided areas arranged on a substrate, the method comprising: making a correction of a movement of the substrate on exposure of a predetermined layer on an assumption that of an exposure already performed on the predetermined layer, a thermal energy generated on an exposure which is performed spatially and temporally close to an exposure performed on the divided area causes a local thermal expansion of the substrate, and a thermal energy generated on an exposure which is performed spatially and temporally far away from the exposure to be performed causes thermal expansion of the substrate in general.
According to this method, in the case it is appropriate to employ the model that thermal expansion due to the thermal energy generated by exposure on a divided area occurs, it first locally occurs in a portion near the divided area and then gradually conducts to the overall substrate. Performing exposure accurately considering the actual thermal expansion of the substrate, thus becomes possible, further improving the overlay accuracy.
According to the fifth aspect of the present invention, there is provided a first exposure apparatus which sequentially transfer a pattern formed on a mask onto a plurality of divided areas arranged on a substrate along a predetermined direction, in an exposure sequence that proceeds to an adjacent divided area in the predetermined direction, the exposure apparatus comprising: a substrate stage which holds the substrate; and a movement control unit which corrects a movement information so as to make a correction amount of a movement amount of the substrate smaller than a correction amount of a movement amount of the substrate on preceding exposure, and adjusting a positional relationship between the mask and the substrate for exposure of a next divided area.
According to this apparatus, the movement control unit corrects the movement information so as to make the correction amount of the movement amount of the substrate smaller than that of the substrate for the preceding exposure. After the positional relationship between the mask and the substrate is adjusted for exposure on the next divided area, exposure is performed. That is, the pattern on the mask can be transferred onto the substrate by exposing the respective divided areas by using the first exposure method of the present invention. This makes it possible to ensure high overlay accuracy.
In the first exposure apparatus according to the present invention, the divided areas can be arranged on the substrate in a shape of a matrix, and the exposure sequence proceeds to the adjacent divided area in a first row direction of the matrix, and when there is no adjacent divided area in the first row direction then goes on to an adjacent row in a column direction of the matrix, and continues in a second row direction, which is opposite to the first row direction, and the movement control unit increases the correction amount of the movement amount of the substrate as exposure sequence proceeds to the adjacent row in the column direction.
This apparatus can further comprise a measuring unit which measures the movement information prior to exposure of the substrate. In this case, the measuring unit comprises: a position detection unit which detects positional information of a plurality of predetermined alignment marks which are among a plurality of alignment marks formed on the substrate with the plurality of divided areas; and a calculation unit which calculates positional information of the plurality of divided areas formed on the substrate by statistical calculation based on a result of the detecting.
In such a case, on multilayer exposure, before actually exposing the second or subsequent layer, the position detection unit detects the positional information of a plurality of predetermined alignment marks which are among a plurality of alignment marks formed on the substrate with a plurality of divided areas. The calculation unit obtains the positional information of a plurality of divided areas formed on the substrate by statistical calculation such as least-squares approximation based on the results of the detection.
Subsequently, the respective divided areas are sequentially exposed. When a new divided area is subject to exposure, the movement control unit corrects the movement information obtained based on the positional information in consideration of the thermal expansion of the substrate. The positional relationship between the substrate and the mask is adjusted according to the corrected updated. movement information.
Multilayer exposure can therefore be performed while maintaining high overlay accuracy, regardless of the exposure sequence for each layer.
The first exposure apparatus according to the present invention can further comprise a configuration of an image characteristic control system which controls an image characteristic of a transferred image of the pattern onto the substrate based on the correction amount of the movement information. In such a case, the image characteristic control system controls imaging characteristics such as the image magnification and image distortion of the pattern on the substrate in accordance with the thermal expansion of the substrate. This makes it possible to reduce the difference between the size of the pattern transferred onto the respective divided areas on the substrate that is cooled after the exposure and suppress distortion.
The structure of the image characteristic control system may vary. For example, the image characteristic control system can comprise: a synchronous moving mechanism which synchronously moves the mask and the substrate on exposure of the divided areas; and a synchronous movement control mechanism which controls at least one of a starting position of the mask which moves synchronously on exposure of the divided area, a starting position of the substrate which moves synchronously, a synchronous velocity ratio between the mask and the substrate, a direction of the mask moving synchronously, a direction of the substrate moving synchronously, and a rotational angle of the mask around a normal to a surface which the patterns are formed, is corrected with respect to the correction amount of the movement information.
In this case, on exposing each divided area by scanning exposure, the difference between the size of the pattern transferred on the respective divided areas on the substrate that is cooled after the exposure can be reduced, and distortion of the transferred patterns can be suppressed. This makes it possible to ensure high overlay accuracy.
In an exposure apparatus using a projection optical system for scanning exposure, it is preferable to control the image magnification of the pattern and imaging characteristics in the non-scanning direction such as by changing the projection magnification of the projection optical system, the distance between the mask and the projection optical system.
According to the sixth aspect of the present invention, there is provided a second exposure apparatus which sequentially transfers a pattern formed on a mask onto a plurality of divided areas arranged on a substrate in a shape of a matrix in a sequence that proceeds to an adjacent divided area in a first row direction of the matrix, and when there is no adjacent divided area in the first row direction then goes on to an adjacent row in a column direction of the matrix, and continues in a second row direction, the second-row direction which is opposite to the first row direction, the exposure apparatus comprising: a substrate stage which holds the substrate; and a movement control unit which corrects a movement information so as to make a correction amount of a movement amount of the substrate larger than a correction amount of a movement amount of the substrate on a preceding movement between rows, and adjusting a positional relationship between the mask and the substrate for exposure of a first divided area on a new row.
According to this apparatus, the movement control unit corrects the movement information to make the correction amount of the substrate larger than the correction amount of the substrate for the preceding exposure. After the positional relationship between the mask and the substrate is adjusted for exposure on the first divided area on the next row, exposure is performed. That is, the pattern on the mask can be transferred onto the substrate by using the second exposure method of the present invention and exposing the respective divided areas. This makes it possible to ensure high overlay accuracy.
By using the exposure method of the present invention in a lithographic process and performing exposure, fine patterns can be formed on a plurality of layers on a substrate with high overlay accuracy. This makes it possible to manufacture high-integration microdevices with a high yield, thus improving the productivity. Therefore, according to another aspect of the present invention, there is provided a device manufacturing method using the exposure method of the present invention.